The overarching goal of this project is to develop and test a dynamic model of the co-evolution of peer networks, health behavior, and psychological well-being, which can be used to better target health interventions. Researchers have long investigated the link between social networks and various aspects of health including depression and health behaviors. However, most of this work has viewed networks as fixed and exogenous. In this project we examine the ways in which health factors may actively influence network creation and evolution over time using recent advances in statistical modeling of dynamic network data. We use data from the National Longitudinal Study of Adolescent Health (AddHealth) and an actor-based model to investigate the relative contributions of social influence and peer selection processes in understanding the interrelationships between peer networks, psychological well-being and health behavior. The findings from this project will serve as a major contribution to the emerging research on social network dynamics as well as to long standing literature on peer effects on health. Specifically, this project makes three innovative contributions: (1) We explicitly model the likelihood of relationships forming based upon individual traits, including health behavior (selection), and differentiate this from changes in behavior as individuals assimilate to their friends (influence). In so doing, we investigate what types of adolescents are more at risk of selecting peers with particular health behavior or conversely are at risk of changing their behavior to conform to friends'behavior. (2) By using AddHealth, we are able to examine these questions in multiple schools that represent a wide range of contexts. (3) We utilize a series of computer simulations, whose parameters are estimated from empirical data, as a means to investigate multiple intervention strategies and evaluate their potential for reducing the prevalence of smoking, alcohol use, and depression. PUBLIC HEALTH RELEVANCE: This project contributes to the public health by enhancing our understanding of the social network dynamics involved in the development of adolescent health behaviors and psychological well-being. The findings have important implications for the development of interventions to reduce adolescent smoking and drinking and improve psychological health.